OAKLEY -- As firefighters leave the East Contra Costa Fire District for more secure jobs elsewhere, those who remain are racking up so much overtime that district officials are starting to worry about both the cost and safety risks.

Ten of the agency's 45 rank-and-file firefighters have quit since February, and two more are on extended leaves -- one to fulfill military duties and the other because of a work-related injury.

The cash-strapped district is trying to keep its five stations open with the 33 firefighters it has left, which means that each is working three additional 24-hour shifts per month on average, said Chief Hugh Henderson.

Apart from the approximately $85,000 that overtime cost in July alone, Director Ron Johansen is wondering how much longer firefighters can hold out before they become so tired that they are injured on the job or start taking sick leave simply to get rest -- thereby creating the need for the district to pay even more overtime.

"That's telling you they've reached their limit physically, emotionally," he said. "You can only ask so much of your firefighters."

Currently, most are volunteering to put in the extra hours, Johansen said, but he thinks the district likely will have to require more to step up.

Many outsiders don't realize how stressful the job is, Johansen added.

"People think that firefighters just sit around all day, and there's no real workload on them on a regular basis," he said.

In reality, the sleep deprivation they experience when responding to several calls a night for days at a time has a cumulative effect and can affect an individual's overall health, Johansen said.

Noting that his men are facing one of the driest summers in California history, Henderson has recommended that the district continue paying overtime to maintain the current staffing levels until it knows the outcome of whatever revenue measure it puts to voters.

Although the board still could decide to place a parcel tax on the November ballot, it's currently considering a benefit assessment. Directors are scheduled to vote whether to proceed with that option early next month.

The cost of keeping all five stations open until voters have weighed in on that proposal Oct. 6 is an estimated $350,000, which would force the district to draw on its reserves.

A benefit assessment would apply to owners of the 43,000-plus parcels in the district, and the election would be decided by a majority vote, each of which would carry more or less weight according to how much benefit that property owner is calculated to receive from fire services.

The amount of the assessment also would vary depending on a number of factors, which could include the size and location of a lot as well as the type of structures on it.

Regardless of whether the district pursues a benefit assessment or a parcel tax, however, it says it will have to close two stations no later than Dec. 1 if voters reject those options.

If it succeeds, on the other hand, it would be able to keep both open in the long run even if it still must close them temporarily because there aren't enough firefighters to continue operations without jeopardizing their safety, said Director Cheryl Morgan.

"It's all a function of how many people are left," she said.

Contact Rowena Coetsee at 925-779-7141. Follow her on Twitter.com/RowenaCoetsee.